feat(lanes): Antigravity lanes, release exited panes, fresh Codex starts

- antigravity: a third lane tool running Antigravity's `agy` CLI. `-i`
  carries the first prompt, `--continue` resumes; `agy` has no model,
  effort or permission flag, and `--dangerously-skip-permissions` is never
  emitted. No pipeline, no agents install, and no AI Router (native only,
  else EUNSUPPORTED). Add lane gains an Antigravity choice and the binary
  probe maps it to `agy`.
- UI: the lane card no longer renders a frame holding only a "Codex" chip,
  and the prompt box names the lane's CLI ("Ask Codex anything…"), via
  LANE_TOOL_LABEL.
- runs: a pane that exits is released on a 10 s server beat
  (healAllRunIds, DASHBOARD_RUN_HEAL_MS). Codex and Antigravity fire no
  hook, so their lanes stayed "running" until something re-read them.
- codex: Start no longer sends resumeLast — only "Resume last session"
  continues the previous thread.

client/src/pages/Workspace.tsx

@@ -395,8 +395,8 @@ export function Workspace() {
   }, [lanes, searchParams, setSearchParams]);
 
   useEffect(() => {
-    Promise.all([api.run.binary("claude"), api.run.binary("codex")])
-      .then(([claude, codex]) => setBinaryStatus({ claude, codex }))
+    Promise.all([api.run.binary("claude"), api.run.binary("codex"), api.run.binary("antigravity")])
+      .then(([claude, codex, antigravity]) => setBinaryStatus({ claude, codex, antigravity }))
       // Fetch failure (server unreachable, proxy misrouted, etc.) isn't proof
       // `claude` or `codex` is missing from PATH — leave the probe unresolved rather than
       // showing a misleading "binary missing" banner for an unrelated fault.
@@ -523,7 +523,8 @@ export function Workspace() {
   }, [refreshList]);
 
   const currentLane = selectedLaneId !== null ? lanes.find((l) => l.id === selectedLaneId) : null;
-  const isCodexLane = currentLane?.tool === "codex";
+  // Only claude lanes carry a pipeline (codex and antigravity emit no hooks).
+  const noPipeline = !!currentLane && currentLane.tool !== "claude";
 
   // Feature list follows the selected lane, resets the viewer on lane switch.
   useEffect(() => {
@@ -816,16 +817,16 @@ export function Workspace() {
                     <Pencil className="h-3 w-3 shrink-0 text-fg-muted opacity-0 transition-opacity group-hover:opacity-100" />
                   </button>
                 )}
-                {/* Codex lanes carry no pipeline: no time-at-stage, no pipeline
-                    or feature picker, no map. */}
-                {!isCodexLane && (
+                {/* Non-claude lanes carry no pipeline: no time-at-stage, no
+                    pipeline or feature picker, no map. */}
+                {!noPipeline && (
                   <span className="shrink-0 tabular-nums text-xs text-fg-muted">
                     {since(currentLane.stage_seconds)}
                   </span>
                 )}
                 {showInfo && (
                   <>
-                    {!isCodexLane && (
+                    {!noPipeline && (
                       <select
                         data-testid="pipeline-picker"
                         aria-label={tLanes("pipelinePicker.label")}
@@ -855,13 +856,14 @@ export function Workspace() {
                         ))}
                       </select>
                     )}
-                    <LaneRouterRow lane={currentLane} />
+                    {/* `agy` has no endpoint to point at a router. */}
+                    {currentLane.tool !== "antigravity" && <LaneRouterRow lane={currentLane} />}
                     {/* No stage chip and no "auto: <stage>" chip here: the
                         PipelineMap right below this header already draws both
                         — the declared node as the current ring, the detected
                         one as its amber badge — so the chips were a second,
                         smaller copy of the same two facts. */}
-                    {!isCodexLane && features.length > 0 && (
+                    {!noPipeline && features.length > 0 && (
                       <select
                         data-testid="feature-picker"
                         className="rounded border border-border bg-surface-1 px-2 py-0.5 text-xs"
@@ -921,7 +923,7 @@ export function Workspace() {
                     onSelectLane={setSelectedLaneId}
                   />
                 </div>
-                {!isCodexLane && (
+                {!noPipeline && (
                   <div className="mb-3">
                     <PipelineMap
                       nodes={